1. Field of the Invention
The invention relates generally to a method for controlling injection rate and injection pressure in an electromagnetic fuel injector. More specifically, the invention relates to a method for controlling injection rate and injection pressure by varying current to a solenoid-actuated control valve to improve the operational characteristics of the fuel injector.
2. Background Art
Fuel injector assemblies are employed in internal combustion engines for delivering a predetermined, metered mixture of fuel and air to the combustion chamber at preselected intervals. In the case of compression ignition engines and diesel engines, the fuel/air mixture is delivered at relatively high pressures. Presently, conventional injectors deliver this mixture at pressures as high as 32,000 psi. These fairly high pressures require considerable engineering attention to ensure the structural integrity of the injector, good sealing properties, and the effective atomization of the fuel within the combustion chamber. However, increasing demands for greater fuel economy, cleaner burning, fewer emissions and NOx control have placed, and will continue to place, even higher demands on the engine's fuel delivery system, including increasing the fuel pressure within the injector.
Fuel injectors presently employed in the related art typically include a high pressure fuel passage, which extends between a solenoid-actuated control valve and the plunger cylinder in the injector body. Fuel at relatively low pressure is supplied to the control valve, which then meters the delivery of the fuel at very high pressures and at predetermined intervals through the high pressure fuel passage to the plunger cylinder. The fuel ultimately exits the injector through a fuel nozzle.
The solenoid-actuated control valve is supported in a stepped bore which typically extends through a side body of the injector. The stepped bore defines a supply chamber and a valve bore. The valve bore receives a valve stem of the associated control valve. The valve bore may terminate in a chamfered valve seat. Similarly, the valve stem may terminate in a head that seats against the valve seat under the force generated by the solenoid. The head is configured to mate closely with the valve seat. At least a portion of the valve stem is subject to the high pressure generated in a valve opening direction during an injection cycle. Accordingly, the solenoid must generate sufficient force in the valve closing direction to overcome such pressure. These forces are borne by the valve seat through the head of the control valve.
While the design and operation of fuel injections have continued to progress, there remains a constant need to improve fuel economy and reduce emissions while at the same time reducing engine noise induced from the operation of the fuel injector.